How to select a particular region in a image, and segment it & compare it ?

Hi all, I'm doing a project on Vacant parking space detection. I can able to detect the change in the entire frame but I want to detect for only particular space. can any one help? Thanks in advance.

video = VideoReader('demo_parking.mp4');
I = read(video,1);
Background = read(video,1);
Background1 =abs(Background - I);
for k = 1:500

      if k== 1
        Background = read(video,1);

    else
        % Change background slightly at each frame
  %       Background(t+1)=(1-alpha)*I+alpha*Background
        Background1 =abs(Background - I);

      end
      I=k;
      k=k+12;
     grayImage = rgb2gray(Background1); % Convert to gray level
      thresholdLevel = graythresh(grayImage); % Get threshold.
      binaryImage = im2bw( grayImage, thresholdLevel); % Do the binarization

         binaryImage = bwareaopen(binaryImage,1000);
         se = strel('square', 5);

        binaryImage=imdilate(binaryImage,se);
figure,imshow(binaryImage);
labeledImage = bwlabel(binaryImage, 8);
stats = regionprops(labeledImage,'BoundingBox','Area');
count=0;
total=8;
for j = 1 : length(stats)

thisBB = stats(j).BoundingBox;
rectangle('Position', [thisBB(1),thisBB(2),thisBB(3),thisBB(4)],...
'EdgeColor','g','LineWidth',1 );
count=count+1;
end
disp(['No of parked vehicles are ',num2str(count)]);
disp(['No of available slots  ',num2str(total-count)]);
end

Answer 1

[Image Analyst]

Use a template. Use roipoly() or roipolyold() to define the spaces on one of the frames. You can save the vertex coordinates in a .mat file if you want.